The research showed that eating a diet supplemented with extra virgin olive oil was associated with a relatively lower risk of breast cancer in a study of women in Spain.
The Mediterranean diet involves lots of vegetables, a splash of wine, fish and especially olive oil.
Lead author Dr Miguel Martinez-Gonzalez, of the University of Navarra in Spain, said: “The results suggest a beneficial effect of a Mediterranean diet supplemented with extra virgin olive oil in the primary prevention of breast cancer.
“Preventative strategies represent the most sensible approach against cancer.”
The researchers analysed the effects of two interventions with the Mediterranean diet, compared with advice to women to follow a low-fat diet.
The study participants were given one litre per week of extra virgin olive oil for themselves and their families or 30 grams of mixed nuts.
The journal Internal Medicine said it involved recruiting 4,282 women, aged 60 to 80, who were at high risk of developing cardiovascular disease rather than breast cancer.
They were randomly assigned to the Mediterranean diet supplemented with extra virgin olive oil, the Mediterranean diet supplemented with nuts or finally a control diet with advice to reduce their dietary intake of fat.
The researchers found that women eating a Mediterranean diet supplemented with extra virgin olive oil showed a 68 per cent relatively lower risk of malignant breast cancer than those who were allocated the control diet.
Meanwhile, women eating a Mediterranean diet supplemented with nuts showed a non-significant risk reduction compared with women in the control group.
The researchers noted a number of limitations in their study including that breast cancer was not the primary endpoint of the trial for which the women were recruited.
They said the study could not establish whether the observed beneficial effect was attributable mainly to the olive oil or to its consumption within the context of the Mediterranean diet.
Doctor Mitchell Katz, deputy editor of Internal Medicine, said despite the limitations, the findings were useful.
“Of course, no study is perfect,” he said. “This one has a small number of outcomes - only 35 incident cases of breast cancer, the women were not all screened for breast cancer with mammography, they were not blinded to the type of diet they were receiving, and all were white, postmenopausal and at high risk for cardiovascular disease.
“Still, consumption of a Mediterranean diet, which is based on plant foods, fish and extra virgin olive oil, is known to reduce the risk of cardiovascular disease and is safe.
“It may also prevent breast cancer.
“We hope to see more emphasis on a Mediterranean diet to reduce cancer and cardiovascular disease and improve health and well-being.”